1. Field of the Invention
The invention is related to automotive safety restraint systems and in particular to an energy absorber connected between a structural member of the vehicle and a member of the safety restraint system.
2. Prior Art
Load limiting or energy absorbing devices are well known in the art for limiting the maximum applied stress and for reducing the ultimate strength requirements of a load restraint system. Most mechanical energy absorbing devices utilize the plastic deformation of a wire or blade in which the deformation forces absorb the energy when it exceeds predetermined limits.
Energy absorbers provide two useful functions in safety restraint systems such as conventionally used in aircraft or automotive vehicles. During a crash condition, energy absorbers reduce the ultimate strength requirement of the safety restraint system, and reduce the maximum loading on the occupant thereby lowering the risk of internal injuries. The requirements for energy absorbers in automotive safety restraint systems is becoming increasingly important as the trend towards smaller vehicles brings about a corresponding increase in the loads being transmitted to the restrained occupants.
One such energy absorbing device presently being used in safety restraint systems is the energy absorber disclosed by Lindblad in U.S. Pat. No. 4,199,190 in which the opposite ends of a length of wire are captivated in a common ferrule. The energy is absorbed by the plastic deformation of the wire as it is pulled through a crimped area of the ferrule. The problem with this type of energy absorber is that its energy absorbtion capabilities are limited by the length of wire contained in the ferrule. Therefore the crimping of the ferrule must be adjusted so that the energy capable of being absorbed is greater than the total energy induced in the system under the severest crash conditions so that neither end of the wire will be pulled free of the ferrule. Unfortunately these constraints limit the lowest breakaway level at which the energy absorber will yield and it has been found that a minimum breakaway level satisfying the above conditions is sufficiently high to pose a higher than desired risk of internal injuries to the occupant.
As an alternative, the minimum breakaway load level could be reduced by decreasing the severity of the crimp in the ferrule and increasing the length of the free ends of the wire. However under higher crash loads, it was found that the extension of the energy absorber, with a reduced breakaway load level, provided excessive slack in the safety restraint system, and the occupant was no longer restrained from forceably engaging the interior parts of the vehicle. Therefore this solution is unacceptable. The invention is an energy absorber which overcomes the problems encountered with this type of energy absorber.